1. Field of the Invention
The invention relates to a vehicle that includes an engagement device (a transmission, a clutch, or the like) between an internal combustion engine and a drive wheel and that includes a differential mechanism (a planetary gear mechanism, or the like), including at least three rotating elements, between the internal combustion engine and the engagement device.
2. Description of Related Art
Japanese Patent Application Publication No. 2006-335127 (JP 2006-335127 A) describes a vehicle that includes a transmission (engagement, device) between an engine and drive wheels and that includes a planetary gear mechanism (differential mechanism) between the engine and the transmission. The planetary gear mechanism includes a sun gear coupled to a first motor, a ring gear coupled to a second motor and the drive wheels via the transmission, pinions meshed with the sun gear and the ring gear, and a carrier coupled to the engine. JP 2006-335127 A describes a technique for, in the above-described vehicle, suppressing a shift shock by controlling the rotation speed of the ring gear with the use of at least one of the first motor and the second motor during shifting of the transmission.
However, in the vehicle described in JP 2006-335127 A, at the time when the rotation speed of the ring gear is controlled during shifting of the transmission, if the power generated by the engine is controlled without considering a variation in the rotation energy of the planetary gear mechanism, the shift may stagnate, with the result that it may not be possible to attain an appropriate shifting time.
That is, in an ordinary engine vehicle in which no planetary gear mechanism is provided between an engine and a transmission, there is a steady positive correlation (correlation in which, as one increases, the other also increases; and, as one decreases, the other also decreases) between the power generated by the engine and a rotation variation in the input shaft of the transmission. Thus, it is possible to facilitate a downshift by increasingly correcting the power generated by the engine and to facilitate an upshift by decreasingly correcting the power generated by the engine.
Incidentally, in a vehicle in which a planetary gear mechanism is provided between an engine and a transmission as in the case of the vehicle described in JP 2006-335127 A, depending on the state of the planetary gear mechanism, the correlation between the power generated by the engine and a rotation variation in the input shaft of the transmission may change and become a negative correlation (correlation in which, as one increases, the other decreases; and, as one decreases, the other increases). Therefore, in the vehicle described in JP 2006-335127 A, if a correction as in the case of the ordinary engine vehicle is performed, a shift in the transmission may stagnate depending on the state of the planetary gear mechanism.